Characteristics of Asian aerosol transport simulated with a regional-scale chemical transport model during the ACE-Asia observation

The transport and optical thickness of tropospheric aerosols (dust, sulfate, carbonaceous aerosols, and sea salt) during the ACE-Asia intensive observation period (spring 2001) were simulated using a CFORS chemical transport model coupled with a regional meteorological model. Simulated aerosol fields were examined intensively with surface monitoring stations (PM₁₀, sulfate, and total carbonaceous aerosol), Mie Lidar, and satellite observation data. It was shown that CFORS aerosol fields agree with observations and reproduced many observed characteristics including the several high concentration levels associated with the continental outflow, aerosol vertical profiles and strong correlation between dust and sulfate transports. We found the presence of the latitudinal gradient of aerosol concentrations from these comparisons. The two-month (March and April) averaged aerosol concentration and AOT fields show this latitudinal gradient more clearly, and indicated that the main dust field is located between 30°N and 45°N, while sulfate and carbonaceous field are mainly dominant from their main sources in central China and Southeast Asia to northern Japan (between 25°N and 45°N). Analyses of aerosol horizontal fluxes were also performed. We found that these distributions are closely related to characteristics of wind field of springtime and that each aerosol has the following transport route; the main dust flow is eastward along the 45°N parallel and is located in the free atmosphere; sulfate and carbonaceous aerosols within the boundary layer has a clockwise and divergent flow pattern over central China, which produce the strong outflow associated with anthropogenic emissions at northern latitudes and constrain the continental outflow at the southern latitude; and carbonaceous aerosols at the upper level (2-6 km) have another transport pathway that is along about 30°N from Thailand and Laos. Regional budgets of tropospheric aerosols showed that total emissions were 105 Tg for dust, 8.3 Tg-SO₂ for sulfur (73% from human activities and 27% from volcanic activities), and 3.07 Tg for carbonaceous aerosols. Dry deposition, gravitational settling, and northward outflow of dust accounted for 33%, 27%, and 14% of total emissions, respectively. Wet deposition, eastward outflow, and dry deposition of sulfur accounted for 33%, 27%, and 21%, respectively. Regarding carbonaceous aerosols, the outflow to the east has the highest fraction (49%), followed by dry deposition (16%) and the outflow to the north (14%).